Curb boxes constitute tubular casings usually having an enlarged lower ball housing for encompassing a buried utility service line valve, such as associated with a gas or water line. The upper end of the curb box includes a cover which is usually substantially flush with the ground surface, and removal of the cover permits an elongated wrench to be inserted into the curb box for valve actuation.
Early curb boxes were formed of cast iron, and in recent years synthetic plastic units have been widely used in view of the resistance provided against corrosion, and curb boxes are often constructed of two pieces, one telescoping within the other, wherein vertical forces applied to the curb box cover are not imposed upon the associated valve or conduit system. An example of a synthetic plastic curb box is shown in the assignee's U.S. Pat. No. 2,931,383.
The housing located at the lower end of the curb box is usually provided with an open end which is inserted over the service line valve. Curb box bell housing are often of non-circular configuration in order to resist torque forces imposed thereon, and it is known to incorporate horizontally disposed surfaces and shoulders to resist vertical movement such as caused by ground freezing. Additionally, it is known to utilize base structure mounted to the lower end of the curb box upon which the valve sits, as shown in the aforementioned patent, and curb box base devices may take a variety of forms as additionally illustrated in the assignee's U.S. Pat. Nos. 3,548,864 and 3,901,271. In prior curb boxes the housing is merely placed within the base, and while previous curb box bases do improve the support of the valve, and aid in supporting the curb box during backfilling, the assembly of the base and curb box housing is not of such strength that the base resists vertical curb box displacement.
Utility service lines are now widely utilizing coiled synthetic plastic conduit, and such conduit inherently resists laying flat in a trench due to torsion forces produced during manufacturing and coiling while hot. When applying a valve to such plastic conduit there is often a tendency for the valve to twist and misalign due to forces imposed thereon by the conduit and existing curb box constructions do not provide sufficient valve support to effectively resist such forces in order to maintain the proper orientation between the valve and curb box.
Metal valves installed upon synthetic plastic conduits have a tendency to "sag" due to the inability of the conduit to adequately support the weight of the valve, as is the case with metal pipe. Accordingly, with the increasing use of synthetic plastic conduit it is important that the curb box relieve the conduit of the weight of the valve in that relative vertical displacement of the valve and conduit may produce shear forces ultimately resulting in leakage.
It is an object of the invention to provide a valve curb box utilizing a base wherein the assembly of the base and curb box housing is easily accomplished, whereby the base is firmly affixed to the housing, is positive in action, and will not inadvertently release.
An additional object of the invention is to provide a curb box and base assembly wherein the curb box housing is firmly connected to the base merely by placing the housing upon the base and pushing downwardly wherein a "snap-on" connection is utilized.
An additional object of the invention is to provide a curb box and base assembly wherein a valve within the housing mounted upon the base is firmly supported against vertical and horizontal movement wherein the valve will not twist within the valve housing due to torsional forces imposed thereon by synthetic plastic conduit, and wherein the base accommodates itself to most valve configurations now being employed with utility service lines.
Another object of the invention is to provide a curb box and base assembly which may be used with both metal and synthetic plastic valves.
An additional object of the invention is to provide a curb box and base assembly employing a snap-on interconnection therebetween wherein relative rotation between the curb box housing and base is resisted, and forces imposed upon the curb box structure by the surrounding earth resists curb box and base rotation, and augment the interconnection of the housing and base components.
In the practice of the invention, a curb box casing having a lower valve bell housing of rectangular horizontal cross section is provided with slots intersecting the housing bottom edge whereby the housing may be placed upon an elongated base member having vertical walls. The interrelationship of the housing side and end surfaces with the base, and the cooperation between the slots and the base, prevent relative rotation of the casing and base about the casing vertical axis. The sidewalls of the housing intermediate slots defined thereon are provided with abutment surfaces or "hooks" adjacent oblique cam surfaces whereby insertion of the housing upon the base causes edges on the base to deflect the housing sides outwardly until the abutment surfaces snap under surfaces on the base thereby producing a positive locking of the casing with the base.
The housing end surfaces are provided with openings intersecting the housing bottom permitting the conduit to enter the housing, and the base is also formed with conduit receiving openings which align with those of the curb box housing. The base is of such configuration to firmly support the valve within the housing, and vertically disposed walls defined upon the base engage the earth to resist torque forces imposed upon the housing by the stresses built into the conduit during manufacture and by the turning of the valve itself.